Spinal intervertebral implant adjustable in situ comprising hard pass point

ABSTRACT

The invention concerns a spinal intervertebral implant ( 200 ) comprising at least an upper element ( 203 ), a lower element ( 205 ), and an intermediate member ( 201 ) adapted to co-operate with the upper and lower elements by helical linking means ( 207, 254 ) including means ( 216 ) forming hard pass points when the helical linkage is carried out.

The invention concerns implants of the intervertebral cage type, or ofthe type for replacement of vertebral bodies, intended for the spinalcolumn.

The document WO 99/56675 discloses an implant intended for thereplacement of vertebral bodies and comprising a first, central elementwith two threads, the pitches of which threads run counter to oneanother. It also comprises two end elements, that is an upper endelement and a lower end element, which can be screwed onto said centralelement. In this way, the implant can be adjusted in situ by rotatingthe central element. Thus, the two end elements, that is the upper endelement and the lower end element, are moved away from one another orcloser to one another depending on the sense of rotation of the centralelement. However, in the case of this maneuver, it is difficult to knowhow the adjustment stands. This entails a maneuvering difficulty insurgical operations, the result being a prolongation of the operatingtime.

It is an object of the invention to make available an implant of theintervertebral cage type, or of the type for replacement of vertebralbodies, which it is possible to adjust in situ in a sufficiently quickand precise manner.

For this purpose, provision is made, according to the invention, for aspinal intervertebral implant comprising at least an upper element, alower element, and an intermediate member which can cooperate with theupper and lower elements via helical linking means which include meansforming hard pass points when the helical linkage is carried out.

Thus, the means forming hard pass points permit indexing of the in situadjustment in a simple and precise manner for the surgeon.

Advantageously, the screwing means comprise at least a helical cam and acam follower which can come into contact with a bearing surface of thecam.

Advantageously, the bearing surface has zones forming the hard passpoints.

Advantageously, the zones forming the hard pass points comprise passpoints protruding from the bearing surface.

Advantageously, the upper pass points are bosses.

Advantageously, the intermediate member comprises the cam.

Advantageously, the intermediate member comprises the cam follower.

Advantageously, the intermediate member can be received in one of theupper and lower elements.

Advantageously, the intermediate member can be received in the other ofthe upper and lower elements.

Advantageously, one of the upper and lower elements can be received inthe intermediate member.

Advantageously, the other of the upper and lower elements can bereceived in the intermediate member.

Advantageously, the helical linkage between the intermediate member andthe upper element has a direction of screwing counter to that of thehelical linkage between the central element and the lower element.

Advantageously, the implant additionally comprises means for blocking inposition at least one of the upper and lower elements relative to theintermediate member.

Advantageously, the means for blocking in position comprise at least onestud.

Advantageously, the stud comprises a part which is eccentric in relationto the main axis of use of the stud.

Advantageously, the stud comprises a part which can be screwed.

Advantageously, the implant comprises means for anchoring the implant invertebral plateaus.

Advantageously, the upper and lower elements can fit into one anotherthrough being of complementary shape.

Advantageously, the upper and lower elements fit into one another withsliding.

Advantageously, each upper and lower element has a general U-shape, theelements being able to fit into one another with the U-shapes inopposition.

Advantageously, with at least one of the upper and lower elementscomprising the cam, said cam has an opening opposite its bearingsurface.

Provision is also made, according to the invention, for a surgicalmethod which comprises the steps of positioning the implant at theimplantation site and adjusting said implant in situ by using thescrewing means between the central element and the end elements, thescrewing means having means which form hard pass points.

Advantageously, the surgical method additionally comprises a step offilling the implant with a substance that promotes bone growth.

Other characteristics and advantages of the invention will becomeevident from the following description of a preferred embodiment of theinvention and of an alternative embodiment given as nonlimitingexamples. In the attached drawings:

FIG. 1 is a view, in three dimensions, of a first embodiment of theinvention in the position of minimum height;

FIG. 2 is a view, in three dimensions, of the first embodiment of theinvention in the position of maximum height;

FIG. 3 is a view, in three dimensions, of one of the bases of the firstembodiment from FIG. 1;

FIG. 4 is a view, in three dimensions, of the intermediate element ofthe first embodiment from FIG. 1;

FIG. 5 is a view, in three dimensions, of a second embodiment of theinvention in the position of minimum height;

FIG. 6 is a view, in three dimensions, of the second embodiment of theinvention in the position of maximum height;

FIG. 7 is a view, in three dimensions, of the intermediate element ofthe second embodiment from FIG. 5;

FIG. 8 is a view, in three dimensions, of one of the bases of the secondembodiment from FIG. 5; and

FIG. 9 is a view, in three dimensions, showing the arrangement of thetwo base elements of the second embodiment from FIG. 5.

A first embodiment of the invention will be described with reference toFIGS. 1 through 4. The implant 400 of the intervertebral cage type inthis present embodiment comprises the following main elements: an upperbase 403, a lower base 407, and an intermediate element 401 which can bereceived with sliding and rotation inside the upper and lower bases.

The intermediate element 401 is a tube having an internal diameter andan external diameter. The wall of the tube comprises a plurality oflongitudinal openings 410 similar to elongate slots. These openings 410have their main dimension parallel to a generatix of the tube formingthe intermediate element and are parallel to one another. The openings410 extend radially from the outer face 411 to the inner face 412, thesefaces delimiting the thickness of the tube forming the intermediateelement 401. This intermediate element 401 thus has an internal hollowspace which extends from an upper face 413 to a lower face 414 and whichis delimited radially by the inner face 412. The internal hollow spacecan receive any osteoconductive or osteoinductive substance thatpromotes bone fusion.

Moreover, the intermediate element 401 comprises a plurality of studs407 protruding outward in a radial direction from the outer face 411 ofthe intermediate element 401. The studs 407 are uniformly distributedabout the circumference of the tube in two groups situated,respectively, near the upper end face 413 and lower end face 414. Eachgroup here comprises three studs 407. Each of the studs 407 has what iscalled a contact surface 474, a plane front face 472 perpendicular tothe surface 474, and engagement means 470. The surface 474 is a surfaceof revolution, here cylindrical, while the face 472 is plane andcircular. The height of the studs 407 is such that, once the implant 400has been mounted, the face 472 is flush with the outer face 473 of thebases 403 and 405, which bases will now be described.

Referring to FIG. 3, the lower base 405 is, here, a tube having an upperface 427, a lower face 426, an outer face 473, and an inner face 471.The internal diameter of the tube is substantially equivalent to theexternal diameter of that forming the intermediate element 401. Thus,upon assembly of the implant 400, the face 471 is in contact with theface 411, and the intermediate element 401 is mounted movably withsliding and rotation on the base 405. The upper face 427 isperpendicular to the axis of revolution of the tube forming the base405. The lower face 426, here substantially parallel to the face 427,comprises a plurality of teeth 422, here profiled with a triangularsection and parallel to one another. The teeth 422 in the present caseform means of anchoring in the vertebral plateaus with which the face426 can come into contact.

The outer face 473 comprises a plurality of openings 450 of helical formwhich extend through the thickness of the wall of the tube forming thebase 405 and which are uniformly distributed about the circumference ofthe base 405. Here, they are three in number. Each opening 450 has asmooth face 452 situated toward the plane face 472 of the base 405 andforming a single ramp. The opening 450 additionally has an oppositesurface 454, facing and substantially parallel to the face 452. Thissurface 454, called a contact surface, comprises a group of severalramps 416, here six in number, of concave form, whose radius ofcurvature is substantially equal to the radius of the surface 474 of thestuds 407 with which the ramps 416 can come into contact during use ofthe implant 400. Each ramp 416 comprises a low end 417 and a high end419. The arrangement of the ramps 416 within the group is such that ahigh end of one ramp forms the low end of the following ramp. The ramps416 a and 416 b, called end ramps, of the group do not have a low end orhigh end, respectively, because their surface continues with the sameradius of curvature in such a way as to tangentially rejoin the face 452and thus complete the opening 450.

Moreover, the outer face 473 of the base 405 comprises a plurality oforifices 430 of circular cross section which are threaded (the thread isnot shown), are situated near the face 427, are uniformly distributedabout the circumference of the base 405, and are able to receive a lock432 which is screwed in. The lock is longer than the thickness of thewall of the base 405 so as to be able to engage in one of the openings410 of the intermediate element 401. The role of the lock 432 is tosecure the assembly of the implant 400, as will be seen later in thedescription.

Similarly, the outer face 473 of the base 405 comprises a plurality oforifices 434 of circular cross section which are smooth, are situatednear the face 426 of the base 405, and are uniformly distributed aboutthe circumference of the base 405. These orifices are able to improvethe communication between the outside and the inside of the implant 400when the latter is in the high configuration, as is illustrated in FIG.8.

The upper base 403 is, in a transverse plane perpendicular to the axisof revolution of the base, the mirror-symmetrical counterpart of thelower base 405 which has just been described in detail. The base 403comprises a plurality of openings 435 symmetrical to the openings 450:each opening 435 comprises a smooth face 436 forming a single ramp, asurface 438, called the contact surface, opposite the face 436 andcomprising a group of a plurality of ramps 408 similar to the ramps 416.The group comprises ramps 408 a and 408 b, called end ramps, whosesurface continues in the same radius of curvature in order totangentially rejoin the face 436. The base 403 additionally comprises aface 424 with anchoring means 422, here teeth similar to those presenton the face 426 and previously described.

At the time of the surgical intervention, the surgeon establishes theaccess route and then prepares the implantation site. He then assemblesthe implant 400 by choosing the intermediate element 401 and also a base403 and a base 405. He joins the bases to the intermediate element. Heplaces the various studs 407 on the element 401 via the helical openings435 and 450. He fills the inside of an implant 400, thus formed, with anosteoinductive or osteoconductive substance. He then places the implant400 in the implantation site. He adjusts the height of the implant 400by turning the intermediate element 401, while the bases 403 and 405 areimmobile because of the anchoring means impacted into the vertebralplateaus delimiting the implantation site. Rotation of the implant 401,on account of the helical linkage joining the intermediate element 401to each base 403, 405, causes the studs 407 to move in their respectiveopenings 435 and 450, their surface 474 passing from one ramp 416, 408to another, thus permitting adjustment of the height of the implant.Once the desired distraction height has been obtained, the surgeonsecures the implant 400 in the distraction position, by using theposition-blocking means 432, then closes his access route. By virtue ofthe discontinuities between the ramps 416, the surgeon knows that eachramp passage corresponds to a fixed increase or decrease in height. Thisindexing of the height adjustment means that the surgeon knows how thedistraction of the implantation site stands.

A second embodiment of the invention will be described with reference toFIGS. 5 through 9. The implant 200 of the intervertebral cage type inthis embodiment comprises three main elements: an upper base 203, alower base 205, and an intermediate element 201. The upper 203 and lower205 bases can be received with sliding and rotation inside theintermediate element 201 in order to form a helical linkage as in theaforementioned first embodiment.

The intermediate element 201 is a tube having an internal diameter andan external diameter. The wall of the tube comprises a first pluralityof openings 210, of helical form, whose helix is screwed in thedirection of rotation of the hands of a clock, downward when its axis isvertical. These openings 210, here numbering two, are uniformlydistributed about the circumference of the tube and are situated nearthe lower end face 250. Likewise, the wall of the tube comprises asecond series of helical openings 211 whose helix is screwed in theopposite direction to the hands of a clock, downward when its axis isvertical. These openings 211, here also numbering two, are uniformlydistributed along the circumference of the tube and are situated nearthe upper end face 251. The openings 210 and 211 each have a bearingsurface 217, 218, respectively. The bearing surfaces can come intocontact with position-blocking means (not shown in the figures), as willbe seen later in the description.

Moreover, near the upper 251 and lower 250 end faces, the intermediateelement 201 comprises a plurality of circular orifices 212 uniformlydistributed about the circumference of the tube and here numbering two.These orifices 212 extend through from the outer face 204 to the innerface 215. Each of the orifices 212 comprises a threaded part 213 and acountersink 214 whose diameter is greater than that of the threaded part213. The thread 213 can cooperate with the thread present on a stud 207,which will be described below. Likewise, the countersink 214 can receivethe head of the stud 207.

Each of the studs 207 comprises a substantially plane and circular face272 in which engagement means 270 are formed, here in the form of ahexagonal socket. Once in place, the stud 207 is flush with the outerface 204 of the intermediate element 201. Moreover, the length of thisstud 207 is much greater than the thickness of the tube forming theintermediate element. This is so that it can come into contact with apart 254 of the upper 203 and lower 205 bases, as will now be described.

Referring to FIG. 8, only the upper base 203 will be described, becausethe lower base 205, in a transverse plane perpendicular to the axis ofrevolution of the base, is the mirror-symmetrical counterpart of theupper base 203 which will now be described in detail. The upper base 203is, here, a tube having an upper face 224, a lower face 225, an outerface 231, and an inner face 234. The external diameter of the tube issubstantially equivalent to the internal diameter of that forming theintermediate element 201. Thus, upon assembly of the implant 200, theface 231 is in contact with the face 215, and the upper base 203 is thusmounted movably with sliding and rotation in the intermediate element201. The lower face 225 is perpendicular to the axis of revolution ofthe tube forming the base 203. The upper face 224, here substantiallyparallel to the face 225, comprises a plurality of teeth 222, hereprofiled with a triangular cross section having concave sides anduniformly distributed in a circle having, as its center, the axis ofrevolution of the tube forming the base 203, and having a diametercorresponding to the mean of the internal and external diameters of saidtube forming said base 203. The teeth 222 in the present case form meansof anchoring in the vertebral plateaus with which the face 224 will comeinto contact. Moreover, the face 224 has a circular orifice 234 with itscenter the axis of revolution of the tube forming the base 223.

The body of the base comprises two extensions forming branches 273 and274. These two extensions are symmetrical to one another, on the axis ofrevolution of the tube forming the base 203. The two extensions 273 and274 delimit, on either side of the axis, two openings which are eachopen toward the lower 225 end face of the base 203, said openingscomprising a first substantially vertical lateral face 233, an upperface 254, a face 235, and a second substantially vertical lateral face232 which is substantially parallel to the first lateral face 233. Theupper face 254 called the contact surface or bearing surface comprises agroup of several ramps 216, here seven in number, of concave shape whoseradius of curvature is substantially equal to the radius of that part ofthe studs 207 with which the face 254 can come into contact upon use ofthe implant 200. Each ramp 216 comprises a low end 236 and a high end237. The arrangement of the ramps 216 within the group is such that thehigh end of one ramp forms the low end of the following ramp; the ramps216 a and 216 b, called end ramps, of the group do not have a high endor low end, respectively, because their surface continues with the sameradius of curvature so as to tangentially rejoin the face 233 and theface 235, respectively. The high and low ends 237, 236 form a pluralityof bosses 219.

Moreover, the branch 273, like the branch 274 too, comprises a radiallyextending through-orifice 230 of circular cross section. This orifice230 can receive the position-blocking means (not shown in the figures)of the implant 200.

Such an arrangement of the branches 273 and 274 of the base 203, and oftheir counterparts on the base 205 which is mirror-symmetrical to thebase 203, as has been indicated above, allows the two bases to be fittedinto one another upon assembly and use of the implant, as is illustratedin FIG. 9. The two bases 203 and 205 are mounted with sliding relativeto one another, the different faces 232 of one of the bases being ableto come into contact with the different faces 233 of the other base,respectively. During this fitting together, each extension penetratesinto one of the openings.

At the time of the surgical intervention, the surgeon, as before,establishes the access route and then prepares the implantation site. Hethen assembles the implant 200 by choosing an intermediate element 201and also a base 203 and a base 205. With the different studs 207 alreadyin place on the intermediate element 201, in the orifices 212, hepositions the two bases by inserting them inside the intermediateelement 201, as is illustrated in FIG. 5, the studs 207 being in contactwith the ramps 216 a of the upper base 203 and of its symmetricalcounterpart of the base 205. The implant is now in its lowerconfiguration. He then fits the position-blocking means (not shown)through the slots 211 and 210, respectively, in the orifices 230 of thebases 203 and 205. The position-blocking means can be studs having athread cooperating with a thread formed in the orifice 230, or studswhich can be fitted with rotation in the orifice 230 and whose headreceived in the slots 210, 211 is eccentric in relation to the axis ofthe orifice 230. Once the implant 200 has been assembled, the surgeonfills the inside of the implant with an osteoinductive orosteoconductive substance. He then places the implant 200 in theimplantation site. Then he adjusts the height of the implant by turningthe intermediate element 201 while the bases 203 and 205 are immobilerelative to the respective vertebrae, on account of the anchoring meansimpacted into the vertebral plateaus which delimit the implantationsite. Rotating the intermediate element 201 causes the studs 207 to movealong the ramps 216 of each of the openings in the bases 203 and 205.The surgeon then uses the position-blocking means, received through theslots 210 and 211, in order to block the implant in position. Thesurgeon then closes the access route.

It is of course possible for numerous modifications to be made to thepresent invention without departing from the scope of the latter.

The faces comprising the anchoring means could be inclined relative to amain perpendicular plane of the implant.

It is possible to conceive of any cam system with cam follower otherthan that described above, without departing from the present invention.

It could also be possible to provide an implant having upper and lowerelements able to fit into one another through being of complementaryform, for example as is illustrated in FIG. 9, without having helicallinkages between the intermediate member and the upper and lowerelements with means forming hard pass points.

1. A spinal intervertebral implant comprising at least an upper element(203; 403), a lower element (205; 405), and an intermediate member (201;401) which can cooperate with the upper and lower elements via helicallinking means (207, 254; 407, 435, 450), characterized in that thehelical linking means include means (216; 408, 416) forming hard passpoints when the helical linkage is carried out.
 2. The implant asclaimed in claim 1, characterized in that the helical linking meanscomprise at least a cam (254; 435, 450) and a cam follower (207; 407)which is able to come into contact with a bearing surface (254; 438,454) of the cam.
 3. The implant as claimed in claim 2, characterized inthat the bearing surface has zones forming the hard pass points (236,237; 417, 419).
 4. The implant as claimed in claim 2 or 3, characterizedin that the zones forming the hard pass points comprise pass points(236, 237; 417, 419) protruding from the bearing surface.
 5. The implantas claimed in claim 4, characterized in that the high pass points arebosses (219; 417, 419).
 6. The implant as claimed in one of claims 2through 5, characterized in that the intermediate member comprises thecam.
 7. The implant as claimed in one of claims 2 through 5,characterized in that the intermediate member comprises the cam follower(207; 407).
 8. The implant as claimed in one of the preceding claims,characterized in that the intermediate member (401) can be received inone of the upper (403) and lower (405) elements.
 9. The implant asclaimed in claim 8, characterized in that the central element can bereceived in the other of the upper and lower elements.
 10. The implantas claimed in one of claims 1 through 7, characterized in that one ofthe upper (203) and lower (205) elements can be received in theintermediate member (201).
 11. The implant as claimed in claim 10,characterized in that the other of the upper and lower elements can bereceived in the intermediate member.
 12. The implant as claimed in oneof the preceding claims, characterized in that the helical linkagebetween the intermediate member and the upper element has a direction ofscrewing counter to that of the helical linkage between the centralelement and the lower element.
 13. The implant as claimed in one of thepreceding claims, characterized in that it additionally comprises means(432) for blocking in position at least one of the upper and lowerelements relative to the intermediate member.
 14. The implant as claimedin claim 13, characterized in that the means for blocking in positioncomprise a stud (432).
 15. The implant as claimed in claim 14,characterized in that the stud comprises a part which is eccentric inrelation to the main axis of use of the stud.
 16. The implant as claimedin claim 14, characterized in that the stud comprises a part which canbe screwed.
 17. The implant as claimed in one of the preceding claims,characterized in that it comprises means (222; 422) for anchoring theimplant in the vertebral plateaus.
 18. The implant as claimed in one ofthe preceding claims, characterized in that the upper (203) and lower(205) elements can fit into one another through being of complementaryshape.
 19. The implant as claimed in claim 18, characterized in that theupper and lower elements fit into one another with sliding.
 20. Theimplant as claimed in claim 18 or 19, characterized in that each lowerand upper element has a general U-shape, the elements being able to fitinto one another with the U-shapes in opposition.
 21. The implant asclaimed in claim 18, 19 or 20 and as claimed in claim 7, characterizedin that, with at least one of the upper and lower elements comprisingthe cam (254), said cam has an opening facing its bearing surface (245).